We are investigating the ectopic synthesis of placental proteins by nontrophoblastic neoplasms because of the link between the mechanisms associated with the derepression of the genes synthesizing embryonic proteins and those involved in neoplastic transformation. Our work has concentrated on two placental membrane proteins: placental alkaline phosphatase (PAP) and the transferrin receptor. We have developed both a radioimmunoassay for PAP and an enzymatic immunoassay which identifies isoenzymes. These techniques have been utilized to identify PAP in various normal and neoplastic cell types. By both metabolic and cell surface labeling techniques, it was shown that both BrdUrd and dibutyryl cAMP produce an increase in the levels of this enzyme as opposed to an increase in its activity. We have also found that serum levels of this protein are elevated in 34% of cigarette smokers as opposed to only 5% of controls in a population of breast cancer patients and normal female controls. Investigation of transferrin receptor has shown its ubiquitous presence on dividing cells. This molecule is a dimer consisting of two identical subunits of 94,000 daltons. Its optimum binding conditions include a range of 0.1 to 0.3 M NaCl and pH 6 to 10. The binding affinity for transferrin when corrected for endogenous ligand is 2.4 x 109 M-1. Peptide mapping has shown that there are no receptor subtypes evidenced in a variety of cell types studied. By use of a library of mouse-human hybrids and an RIA, the gene for the transferrin receptor was shown to be localized to chromosome 3. Fluorescence-labeling techniques demonstrated that receptor and ligand co-migrate and are internalized by K562 cells. Electron microscopy demonstrated receptosome-type vesicles consistent with this internalization. In a tumor model, transferrin receptor levels were shown to be elevated in neoplasms of the human breast as opposed to normal tissue. The level of transferrin receptor was shown to be inversely correlated with the level of estrogen receptor in infiltrating ductal carcinoma.